The in vitro and in vivo reaction of adult and neonatal rabbit lymphoid cells and their products to Shope fibroma virus (SFV) and virus induced tumors will be studied. The Madison and Petuxant strains of Shope fibroma virus will be used. Fractionation procedures developed and characterized in this laboratory will be used to study the ability of "T" or "B" analogues to respond to SFV infected targets. Specific killing responses will be measured by using a 51Cr release mediated lymphocytotoxicity assay against established and primary lines of rabbit kidney and fibroblasts. Organ surveys of lymphocytes from infected adults and neonates will be used to determine the distribution of effector cells relative to tumor site. Spleens from neonatally thymectomized animls will be assayed at adulthood in the CML system to characterize the role of thymus in the adult response to virus induced tumors. Immune sera taken from tumor bearing and regressor adults will be used to study blocking or enhancing effector activity in vitro as well as the direct effect of antibody and complement on virus infected cells. These studies should define the role of the immune response of the rabbit to a viral tumor. Since the rabbit has not been previously studied in this regard, further insight into species differences in tumor immunity is expected.